Discharge of solid particles from centrifugal machines

ABSTRACT

A method and apparatus for modifying the flight of particles discharged from the lip of the basket of a centrifugal machine. A pneumatic zone is created around the lip of the basket, and a series of gaseous jets are directed into this zone so as at least to reduce the radial component of velocity, considered in a direction radially outwardly of the basket, of particles discharged from the basket lip. The particles may be allowed to fall, under the influence of gravity, from the pneumatic zone, or alternatively may be pneumatically conveyed from the centrifugal machine.

United States Patent Grimwood et al.

[4 1 Mar. 21, 1972 DISCHARGE OF SOLID PARTICLES FROM CENTRIFUGAL MACHINES Geoffrey L. Grimwood, Holmfirth; Duncan C. Ferrier, Tiverton, both of England Thomas Broadbent & Sons Limited, Huddersfield, Yorkshire, England Filed: Nov. 13, 1969 Appl. No.: 876,229

Inventors:

Assignee:

Foreign Application Priority Data Nov. 16, 1968 Great Britain ..54,475/68 US. Cl ..233/13, 233/46, 127/19, 127/56, 210/369 Int. Cl ..B04b 15/08 Field of Search ..233/12,13,14,15,16,1R, 233/46; 127/17, 19, 56; 210/369, 382; 209/139 A, 144, 145

References Cited UNITED STATES PATENTS 1/1899 Skinner ..233/I3 2,992,140 7/1961 Gaicnnie et a1 ..l27/56 3,011,696 12/1961 Boyland ...233/l3 X 3,301,708 11/1967 Von Rotel ...l27/l9 2,331,850 10/1943 Smith .209/145 3,107,217 10/1963 Muller. ....210/331 3,238,063 3/1966 Steele ..210/369 X Primary Examin eF-James R. Boler Assistant Examiner-George H. Krizmanich Attorney-Beveridge & De Grandi [57] ABSTRACT A method and apparatus for modifying the flight of particles discharged from the lip of the basket of a centrifugal machine. A pneumatic zone is created around the lip of the basket, and a series of gaseous jets are directed into this zone so as at least to reduce the radial component of velocity, considered in a direction radially outwardly of the basket, of particles discharged from the basket lip. The particles may be allowed to fall, under the influence of gravity, from the pneumatic zone, or alternatively may be pneumatically conveyed from the centrifugal machine.

22 Claims, 8 Drawing Figures PATENTEUMAR 21 I972 SHEET 1 [IF 3 GCOFFREY LUTHER Gmmwoc-o4 DUNCAN CAMERON FZRRIIR wi e @oi d W PATENTEUMARZ] I972 3,650,465

SHEET 2 [1F 3 A-A *F/G. 8*

INVENTORS' GEOFFREY LUTHER GR|MWOOD TDUNcAN CAMERON FERRIER PAIENTEMAR21 I972 3 650 465 SHEET 3 BF 3 bBOOODOOOO 000000000 Giormzy urruerz GRmuooog DISCHARGE OF SOLID PARTICLES FROM CENTRIFUGAL MACHINES The present invention relates to centrifugal machines and is particularly concerned with the discharge of particles from the baskets of centrifugal machines such as centrifuges and centrifu gal separators.

A centrifugal machine consists of a centrifuge basket commonly in the form of a perforated hollow cone which basket is rotatably mounted at its apex on a set of bearings. The machine includes a drive mechanism such as an electric motor, for driving the centrifuge basket. When the electric motor is operated and has brought the basket up to a preselected speed, slurry to be separated is introduced into the centrifuge basket. As the basket rotates the slurry separates, in known manner, into a liquor component and a solid particle component. The liquor component passes through the perforations in the basket to be collected in a tank, or other collection vessel, and the solid particle component passes over the peripheral edge or lip of the basket to be discharged substantially tangentially therefrom.

A substantially cylindrical casing is spaced around the lip of the centrifuge basket, and the solid particle component of the slurry which as been discharged from the basket is arrested by this casing. Thereafter the solid particle component falls, under the influence of gravity, into a suitable collection vessel, often located outside the centrifugal machine itself. It will be appreciated that the centrifugal machine can be mounted at any angle, but normally it is arranged either horizontally or vertically for convenience ofloading of the centrifuge basket.

One disadvantage with known centrifugal machines is that the solid particle component tends to strike the casing at speed. This often fractures individual particles, breaking them into smaller particles or fines. The above disadvantage is particularly troublesome when the solid particles being separated are crystals.

A further disadvantage is that the solid particle component has tended to lodge in the walls of the cylindrical casing, thereby both reducing the number of particles collected, and also damaging the casing. According to the present invention there is provided a method of modifying the flight of solid particles discharged from a centrifuge basket lip which comprises directing a series of gaseous jets into a pneumatic zone extending around the basket lip so as at least to reduce the radial component of velocity, considered in a direction radially outwardly of the basket, of particles discharged from said lip.

Thejets may be directed so as to cause the particles to move around the basket, either in the direction of rotation of the basket, or in the opposite direction. Alternatively the jets may be directed so as to directly oppose the flight of the particles from the basket lip.

In one embodiment of the invention for high velocity particles", i.e., particles which are discharged from the centrifuge basket at high speed, thejets may be directed at an acute angle to the tangential direction from the basket lip so as not only to reduce the particle speed in the direction tangentially away from the basket lip but also to reverse the component of velocity of the particles in the circumferential direction of the basket to cause the particles to move around the basket in the opposite direction of rotation thereof.

In a second embodiment of the invention for low velocity particles, i.e., particles discharged from the basket lip at lower speeds thejets of air may have a lower velocity and may be directed at an angle which is related to the tangential direction from the rotor lip so as to afford to the jets a component of velocity which reduces the particle speed in the tangential direction away from the lip and also a component of velocity which serves to change the direction of flight of the particles to cause them to flow circumferentially in the direction of rotation of the basket.

Inthe cases of both high and low velocity discharge, the separated particles may be pneumatically conveyed away fromthe centrifugal machine. In some instances it may be advantageous to provide an auxiliary gas supply to assist in the conveying of the particles.

In a third embodiment of the invention the jets of air may be arranged to have a velocity exactly equal and opposite to that of particles discharged from the centrifuge basket. In this embodiment of the invention the velocity of separated particles is reduced and the particles allowed to drop, under the influence of gravity, from the pneumatic zone.

According to another aspect of the present invention there is provided a centrifugal machine in which the centrifuge basket is surrounded by a hollow casing defining a pneumatic zone, the inner periphery of which casing is open to a discharge lip on said basket for receiving particles discharged therefrom, and the outer periphery of which casing is connected to a manifold surrounding said casing, and means for establishing a series of jets of gas from said manifold to said pneumatic zone which jets are directed so as at least to reduce the radial component of velocity, considered in a direction radially outwardly of the basket, of particles discharged from said lip.

Preferably the means for establishing the jets of gas comprises a plurality of guide vanes located between the manifold and the casing.

The vanes may be arranged in a shallow annular passage connecting the inner periphery of the manifold with the outer periphery of the casing. The vanes may be angled to the radial plane to impart to the jets of air the: required radial and circumferential velocity components to retard and/or deflect the particles, the radial velocity component being directed inwards towards the rotor and the circumferential velocity component either in or against the direction of rotation of the basket. The vanes may be straight or curved in a similar manner to turbine blades.

The casing may be of gradually increasing cross-sectional area in a direction leading towards an outlet therefrom. (See dotted line in FIG. 1). For example the casing may be of volute form. Alternatively the casing may increase in crosssection abruptly towards an outlet. (See FIG. 8). To maintain the flow of the gas and the solid particles component of the slurry, around the casing, a partial vacuum (by vacuum pump at 37 in FIG. 1), may be applied to the discharge end of the casing and/or gas under positive pressure may be admitted to the casing at one or more localities therealong.

The present invention not only reduces impact damage to centrifuged particles but also provides a simple mode of conveying centrifuged particles away from the centrifuge in a gas stream. Further the air or other gas used in the performance of the present invention may be heated in order to dry the particles incidentally with their retardation and/or their conveyance.

The invention together with advantages and features thereof, will be best understood from the following description when read in conjunction with the accompanying drawings.

In the drawings:

FIG. 1 is a partly cut-away perspective view of part ofa centrifugal machine embodying one embodiment of the invention;

FIG. 2 is a sectional elevation on the lines IIII of FIG. 1;

FIG. 3 is a partly cut-away plan view of the centrifugal machine illustrated in FIGS. 1 and 2;

FIGS. 4 and 5 are views similar to FIGS. 1 and 3 ofa second embodiment of the invention,

FIG. 6 is a view similar to FIG. 5 illustrating a modification; and

FIG. 7 is a side sectional view illustrating a centrifugal machine embodying a third embodiment of the invention.

FIG. 8 is a side sectional view through Section A-A in FIG. 1 depicting the abrupt increase in cross-section ofthe casing.

In FIGS. 1 to 3 there is shown a rotatable centrifuge basket 2 ofa centrifugal machine which as a peripheral edge or lip l. The basket 2 is in the form ofa perforated hollow cone and is mounted for rotation on a set of bearings (not shown). Typical perforations are shown in the basket 2 of FIG. 7. The centrifugal machine includes an electric motor (not shown) for driving the basket 2 in the direction of the arrow 10.

A hollow annual casing 3, defining a pneumatic zone 30, is arranged to extend around the basket 2. The inner periphery of the casing 3 is open to the lip l of the basket 2 for receiving particles discharged from the lip in a manner to be described hereafter. The outer periphery of the casing 3 is connected by a shallow annular passage 4 with the inner periphery of a toroidal manifold 5. A plurality of steel vanes 6 are mounted in the passage 4, the vanes being directed at an acute angle with respect to tangents taken from the basket 2.

Pressurized air, or other gas, is introduced into the toroidal manifold 5 from a duct 32 and the air distributes throughout the manifold 5 in known manner. If desired, the air may be heated to assist in the drying of particles separated by the basket 2. The pressurized air passes between the vanes 6 to create a series ofjets of air, which are directed into the pneumatic zone 30, at an acute angle to tangential planes taken with respect to the lip 1 ofthe basket 2.

The casing 3 is of volute configuration, the deepest end of the volute leading to a conveyor duct 34 for conveying separated particles away from the centrifugal machine.

In operation, the electric motor is operated to take the basket 2 up to a selected speed of rotation. Slurry is then introduced into the basket 2 by an inlet pipe (not shown 36. As the basket rotates the slurry separates, in known manner, into a liquor component, which passes through the perforations in the basket 2 to be collected in a tank, (not shown) and a solid particle component. The solid particle component is discharged, substantially tangentially from the lip 1 into the pneumatic zone 30, when it comes under the influence of the jets of air which are defined between the vanes 6.

The action of the jets of air upon the solid particle cmponent will be best understood with reference to FIG. 3 which illustrates the path 11 taken by a single particle after its discharge from the lip 1. Immediately the particle leaves the lip 1 its radial component of velocity is of course zero, but the radial component increases rapidly so that, in the absence of the jets of air, the particles would strip the casing 3 with a high radial velocity component, in the manner of the prior art. However, the jets of air are arranged to have a higher velocity than that ofthe particles and the jets not only reduce the particles speed in the direction tangentially away from the lip 1 but also reverse the component of velocity of the particle in the circumferential direction of the basket. The particle is thus caused to move around the basket 2, as indicated by dotted line 7, in the opposite direction to the direction of rotation of the basket 2.

The particle passes around the volute casing 3, and falls from the pneumatic zone 30, eventually to be removed from the centrifugal machine by the conveyor duct 34, for drying or packaging. If desired, heated air may be passed into the manifold 5, thus assisting in the drying of the particle components.

The embodiment described hereinabove is particularly suitable for centrifuging high velocity particles. A typical use for the embodiment is in the extraction of sugar crystals from low grade massecuite. Here a 30 inch diameter basket is used which is rotated at approximately 1,800 r.p.m. imparting a speed of approximately 250 ft./sec. to each crystal as it leaves the basket.

The embodiment of the invention illustrated in FIGS. 4 and is very similar to that illustrated in FIGS. 1 to 3 and accordingly like reference numerals have been used to designate like parts with those of FIGS. 1 to 3. As compared with the vanes 6 of the first embodiment illustrated in FIG. 1 to 3, vanes 14 of FIGS. 4 and 5 are angled at an obtuse angle to the tangential direction of flight of the particles from the basket lip 1 so as to oppose the flight of the particles in the radially outward direction and to enhance the flight of the particles in the circumferential direction to cause them to move circumferentially around the casing 3 in the direction of rotation of the basket 2, as illustrated in FIG. 5. In this case the casing 3 is much shallower and itself provides the shallow annular passage in which the vanes 14 are located. The flight of the particles as modified by jets of air issuing from between vanes 14 is indicated by the broken line 15.

The embodiment illustrated in FIGS. 4 and 5 is particularly suitable for low velocity particles, for example, in the separation of balls, such as polystyrene balls at a velocity of approximately ft./sec.

FIG. 6 illustrates a form of construction which is similar to that of FIGS. 4 and 5 except that it incorporates vanes 16 which are curved, in a similar way to turbine blades, instead of being straight. Curved vanes could of course be used in the embodiment of FIGS. 1 to 3 instead of straight vanes.

One advantage of curved blades is that the pressurized air from passing the manifold 5 is gradually deflected, and this tends to reduce the pressure drop across the vanes.

The third embodiment of the invention illustrated in FIG. 7 is similar to the first embodiment and again like reference numerals have been used to designate like parts with those of FIGS. 1 to 3. The casing 3 is shallow over its inner periphery surrounding the lip l, but its outer periphery adjacent the shallow passage 4 is deep to enable particles arrested by the jets of air to flow freely under gravity as illustrated by the broken lines 24. The particles flow through the casing 3 to a storage container, or to a conveyor.

In this embodiment of the invention the jets of air are arranged to have a velocity substantially equal and opposite to that of particles discharged from the lip 1. The velocity of separated particles is thus reduced and the particles fall, under the influence of gravity, from the pneumatic zone 30 into a container or onto a conveyor. The liquor component is removed through a pipe 25 in known manner.

It will be appreciated that while in the above described embodiment of the invention the gas used for providing the jets has been air, that any gas could be used. Furthermore, if the pressure of gas from the jets proves insufficient to pneumatically convey separated particles through the conveyor duct 34, an additional gas supply could be provided for assisting in conveying the particles such as at 35 in FIGS. 6 and 7.

Again it will be apparent to persons skilled in the art that whilst the above described embodiments have described vanes for producing the required gas jets, other mechanical constructions, such as a plurality of bores between the manifold and easing, could be used.

While the invention has been described with reference to particular embodiments thereof it is to be understood that modifications may be made by persons skilled in the art without departing from the spirit of the invention or from the scope of the invention defined in the appended claims.

We claim:

1. In a process of discharging particles from a centrifugal machine having a rotating centrifuge basket with a lip, a method of modifying the flight of solid particles discharged from the lip of said centrifuge basket, said particles having a radial component of velocity considered in a direction radially outwardly of the basket, wherein the improvement comprises creating a pneumatic zone extending around said basket lip and directing a series ofjets of gas into said pneumatic zone so as at least to reduce the radial component of velocity of the particles discharged from said lip.

2. The process as set forth in claim 1 consisting essentially of directing the jets ofgas at an acute angle relative to tangential planes taken with respect to the basket lip, said jets of gas being adapted to have a velocity sufficient to both reduce the particles speed in said tangential planes and to reverse the component of velocity in a circumferential direction around the basket whereby to cause the particles to move around the basket in the opposite direction to the direction of rotation of the basket.

3. The method as set forth in claim 1 consisting essentially of directing the jets of gas at an obtuse angle relative to tangential planes taken with respect to the basket lip, said jets of gas being adapted to have a velocity sufficient to both reduce the particles speed in said tangential planes and to cause the particles to move around the basket in the direction of rotation of the basket.

4. The method as set forth in claim 1 consisting essentially of pneumatically conveying separated particles away from the machine.

5. The method as set forth in claim 4 consisting essentially of introducing auxiliary gas into said pneumatic zone for assisting pneumatic conveyance of the particles.

6. The method as set forth in claim 5 consisting essentially of heating said auxiliary gas.

7. The method as set forth in claim 1 which consists essentially of directing the jets of gas substantially opposite to tangential planes taken with respect to the basket, said jets being adapted to have a velocity substantially equal to that of particles discharged from said basket.

8. The method as set forth in claim 1 which consists essentially of heating said first-mentioned gas.

9. A centrifugal machine having a perforated frustoconical centrifugal basket with a discharge lip and including means for introducing into said basket slurry to be separated, wherein the improvement consists essentially of:

a stationary hollow casing surrounding said basket which casing defines an annular pneumatic zone around said lip, said casing having an outlet,

a toroidal manifold forming part of said casing and surrounding said pneumatic zone,

means for introducing a pressurized gas into said manifold,

a shallow annular passage between said casing and said manifold,

means located within said passage for establishing a plurality ofjets of gas directed into said pneumatic zone, which jets of gas are directed so as at least to reduce a radial component of velocity, considered in a direction radially outward of said basket, of solid particles separated from said slurry and discharged over said lip, while said particles are located in said pneumatic zone.

10. A centrifugal machine as set forth in claim 9 wherein the means for establishing the plurality ofjets of gas comprises a plurality of guide vanes.

11. A centrifugal machine as set forth in claim 10 wherein the vanes are angled at an acute angle relative to tangential planes taken with respect to the basket lip.

12. A centrifugal machine as set forth in claim 10 wherein the vanes are angled at an obtuse angle relative to tangential planes taken with respect to the basket lip.

13. A centrifugal machine as set forth in claim 10 wherein the vanes lie in substantially tangential planes taken with respect to the basket lip.

14. A centrifugal machine as set forth in claim 13 wherein the casing has an inner periphery surrounding and adjacent to said lip, and an outer periphery adjacent to said shallow annu lar passage, said outer periphery being deeper than said inner periphery.

15. A centrifugal machine as set forth in claim 10 wherein the vanes are straight.

16. A centrifugal machine as set forth in claim 10 wherein the vanes are curved.

17. A centrifugal machine as set forth in claim 9 wherein the casing is of gradually increasing cross-sectional area in a direction leading towards the outlet.

18. A centrifugal machine as set forth in claim 17 wherein the casing is of volute form.

19. A centrifugal machine as set forth in claim 17 wherein the casing increases in cross section abruptly towards the outlet.

20. A centrifugal machine as set forth in claim 17 wherein a conveyor duct is provided at the outlet to said casing for pneumatically conveying separated particles from said centrifugal machine.

2]. A centrifugal machine as set forth in claim 20 wherein additional gas means are provided for assisting the flow of particles along said conveyor duct.

22. A centrifugal machine as set forth in claim 20 wherein reduced pressure means are provided for applying a reduced pressure to the end of said conveyor duct remote from said centrifugal machine. 

1. In a process of discharging particles from a centrifugal machine having a rotating centrifuge basket with a lip, a method of modifying the flight of solid particles discharged from the lip of said centrifuge basket, said particles having a radial component of velocity considered in a direction radially outwardly of the basket, wherein the improvement comprises creating a pneumatic zone extending around said basket lip and directing a series of jets of gas into said pneumatic zone so as at least to reduce the radial component of velocity of the particles discharged from said lip.
 2. The process as set forth in claim 1 consisting essentially of directing the jets of gas at an acute angle relative to tangential planes taken with respect to the basket lip, said jets of gas being adapted to have a velocity sufficient to both reduce the particles'' speed in said tangential planes and to reverse the component of velocity in a circumferential direction around the basket whereby to cause the particles to move around the basket in the opposite direction to the direction of rotation of the basket.
 3. The method as set forth in claim 1 consisting essentially of directing the jets of gas at an obtuse angle relative to tangential planes taken with respect to the basket lip, said jets of gas being adapted to have a velocity sufficient to both reduce the particles'' speed in said tangential planes and to cause the particles to move around the basket in the direction of rotation of the basket.
 4. The method as set forth in claim 1 consisting essentially of pneumatically conveying separated particles away from the machine.
 5. The method as set forth in claim 4 consisting essentially of introducing auxiliary gas into said pneumatic zone for assisting pneumatic conveyance of the particles.
 6. The method as set forth in claim 5 consisting essentially of heating said auxiliary gas.
 7. The method as set forth in claim 1 which consists essentially of directing the jets of gas substantially opposite to tangential planes taken with respect to the basket, said jets being adapted to have a velocity substantially equal to that of particles discharged from said basket.
 8. The method as set forth in claim 1 which consists essentially of heating said first-mentioned gas.
 9. A centrifugal machine having a perforated frustoconical centrifugal basket with a discharge lip and including means for introducing into said basket slurry to be separated, wherein the improvement consists essentially of: a stationary hollow casing surrounding said basket which casing defines an annular pneumatic zone around said lip, said casing having an outlet, a toroidal manifold forming part of said casing and surrounding said pneumatic zone, means for introducing a pressurized gas into said manifold, a shallow annular passage between said casing and said manifold, means located within said passage for establishing a plurality of jets of gas directed into said pneumatic zone, which jets of gas are directed so as at least to reduce a radial component of velocity, considered in a direction radially outward of said basket, of solid particles separated from said slurry and dischargEd over said lip, while said particles are located in said pneumatic zone.
 10. A centrifugal machine as set forth in claim 9 wherein the means for establishing the plurality of jets of gas comprises a plurality of guide vanes.
 11. A centrifugal machine as set forth in claim 10 wherein the vanes are angled at an acute angle relative to tangential planes taken with respect to the basket lip.
 12. A centrifugal machine as set forth in claim 10 wherein the vanes are angled at an obtuse angle relative to tangential planes taken with respect to the basket lip.
 13. A centrifugal machine as set forth in claim 10 wherein the vanes lie in substantially tangential planes taken with respect to the basket lip.
 14. A centrifugal machine as set forth in claim 13 wherein the casing has an inner periphery surrounding and adjacent to said lip, and an outer periphery adjacent to said shallow annular passage, said outer periphery being deeper than said inner periphery.
 15. A centrifugal machine as set forth in claim 10 wherein the vanes are straight.
 16. A centrifugal machine as set forth in claim 10 wherein the vanes are curved.
 17. A centrifugal machine as set forth in claim 9 wherein the casing is of gradually increasing cross-sectional area in a direction leading towards the outlet.
 18. A centrifugal machine as set forth in claim 17 wherein the casing is of volute form.
 19. A centrifugal machine as set forth in claim 17 wherein the casing increases in cross section abruptly towards the outlet.
 20. A centrifugal machine as set forth in claim 17 wherein a conveyor duct is provided at the outlet to said casing for pneumatically conveying separated particles from said centrifugal machine.
 21. A centrifugal machine as set forth in claim 20 wherein additional gas means are provided for assisting the flow of particles along said conveyor duct.
 22. A centrifugal machine as set forth in claim 20 wherein reduced pressure means are provided for applying a reduced pressure to the end of said conveyor duct remote from said centrifugal machine. 